The compounds that dissolve in water to form OH – ions and ions or molecules that absorb hydrogen ions from acid are called bases. The bases are classified as weak bases and strong bases on the basis of the strength that they carry. 

The base that does not dissolve completely but some particles that remain in the solvent are called weak bases.

What are weak bases?

When dissolved in a solution, a base that does not dissolve in the given constituent ion but some particles remain is called a weak base. The conjugate acid and the weak base both compose the aqueous solution. 

Hydroxide anions and conjugate acid are formed when the weak base is dissolved in the solution. Some particles remain in the solution undissociated. 

The following equilibrium is created when a weak base is dissolved in the solution:

B plus H2O? BH plus OH-

A hydroxide ion is formed when a single electron pair is contained in the basic molecule and accepts the proton present in the water molecule. The larger concentration on the left of the equilibrium makes the base weak.

Classification of bases

Bases are classified into various categories depending upon several factors. Some of the major classification based on different factors for weak base classification is discussed below:

1. Based on Concentration

• Diluted base: The aqueous solution that contains a comparatively lesser quantity of base in the solution is referred to as a diluted base. Some of the diluted base examples are dilute potassium hydroxide, dilute ammonium hydroxide, and dilute sodium hydroxide.

• Concentrated base: When the aqueous solution has a comparatively higher percentage of the quantity of base in the solution, it is termed as a concentrated base. Examples of the concentrated base include concentrated potassium hydroxide, concentrated ammonium hydroxide, concentrated sodium hydroxide and many more.

2. Based on Strength

• Weak base: When the base does not dissolve completely in the solution, it is called the weak base. Example Zn (OH) 2, NH3

• Strong Base: When the base completely dissolves in the solution it is called the strong base. Example NaOH, KOH, and others

 

3. Based on Acidity of bases

• Triacidic base: When three hydrogen ions combine with three hydroxyl ions, it is a triadic base. Some of the examples include Ferric hydroxide, aluminium hydroxide and others

• Diacidic base: When two hydrogen ions combine with two hydroxyl ions, it is called a diacidic base. Some of the examples include copper ( II ) hydroxide, calcium hydroxide and others
• Monoacidic base: When one hydrogen ion combines with one hydroxyl ion, it is called a monoacidic base. Some of the examples include Ammonium hydroxide, sodium hydroxide and others

Ionization of weak base

An arrow that points from left to right in the given equation represents the sign of reaction for a strong base that is ionized in water. On the other hand, a double arrow in the given equation represents the reaction for a weak base classification. 

The double arrow indicates both reverse and forward reactions are in equilibrium. The hydroxide ion, conjugate acid and the weak base are present in the aqueous solution of a weak base at equilibrium.

Application of bases

There are some critical applications of weak bases in chemistry reactions, physiological purposes, and biochemical studies. The role of a weak base in buffer solutions makes the weak base preferable. Weak bases also perform catalyzing of certain reactions, such as enolate formation.

Some of the application of bases include:

1. Ammonium Hydroxide: It is used in making dyes, plastics, rayon and fertilizers and even act as a reagent in a chemical laboratory.
2. Sodium Hydroxide: This is amongst the important ingredients in the manufacture of detergents and soap.
3. Calcium Hydroxide: Mortar and whitewash processes are not possible without calcium hydroxide
4. Magnesium Hydroxide: The excessive acidity in the human stomach is curtailed by magnesium hydroxide when used as an antacid.

Examples of Weak Base

1. Ammonia (NH3)

A single covalent nitrogen atom, when bonded with three hydrogen atoms, forms ammonia. Ammonia is an inorganic compound, colourless gas and has a very typical pungent smell. When dissolved in water, it segregates into hydroxide ions and ammonium cation. 

Molar mass – 78 g/ mol

Boiling point – – 33.34 degrees Celsius

Density – 2.42 kg/m3

Melting point – 300 degrees Celsius

2. Trimethylamine (N (CH3) 3)

When ammonia reacts with methyl with the catalyst, the compound and weak base trimethylamine are formed. The chemical reaction between ammonium chloride and paraformaldehyde also creates this compound.

Molar mass – 59.11 g/mol

Boiling point – 2.9 degrees Celsius

Density – 670 kg/m3

3. Pyridine (C5H5N)

This is a weak base chemical compound with a structure of heterocyclic. The structure of pyridine is similar to benzyne. A single nitrogen atom replaces one of the methyne groups. Pyridine is a colourless liquid and has a Lewis base behaviour. It can donate electron pairs to the acids of Lewis.

Molar mass – 79.1 g/mol

Density – 982 kg/m3

Boiling point – 115.4 degrees Celsius

Final words

Weak base ionizes in water partially and produces a very small amount of hydroxide ions. The effect on pH of weak bases is less dramatic. Some of the examples include copper hydroxide, ferric hydroxide, zinc hydroxide, pyridine, ammonia and many others. 

Frequently Asked Questions

1. Is water a weak base?

Since a very small amount of water segregates into hydroxide anions and protons, pure water is a weak base and weak acid. The remaining water molecules bind to form hydroxide ions and hydronium ions.

2. State properties of the base

Some of the major properties of the base are mentioned below:

• Red litmus is turned to blue with base
• The taste of the base is bitter
• Bases have the soapy and slippery form
• Some of the bases are good conductors of electricity
• Is sodium hydroxide a weak base

Sodium hydroxide is not a weak base. The formula of sodium hydroxide is NaOH, and it is a chemical compound with a strong base. When dissolved in water, the complete ionization of sodium hydroxide takes place. Therefore it is called a strong base.

Plagiarism Report –